Screw propeller



Jan.'4, 1938. G. H. McLEoD' 2,104,306

` l SCREW PROPELLER FiledJune 20, 1936 l Patented Jan. 4, 1938 f YUNITED STATES PATENT OFFICE f Application'. June zo', 1936, serial No.86,40() In Newprzealana July 1.o, 1935 Y 6 Claims. (Cl. 170-170) -Theinvention relates to screwpropellers used more or less usual form,andextending radially on power driven boats of all descriptions,aerofrom the boss 2, rotating through an inner zone, planes and likemachines, and also to power while outer blades or extensions 3from theexdriven fans and the like. Y tremitiesof the main blades I, rotatethrough an 5 The object of the invention `is to provide` an outer zone,whereby a plurality of working sur- 5 improved form of screw propelleror fan,vdesigned faces is provided beyond the radii of the main' toattain a greater degreeof emciency in operablades and resulting in thepropeller being formed tion, than known forms of propellers. with duplexblade units. y

A propeller made according to the invention, The extension from theextremity of a main is formed with a plurality of working surfaces,blade I to form an outer blade 3, is in a direction 10 provided by mainblades extending radially from outwards from the main blade along saidextremthe propeller boss, and by outer blades extending ity,at therequired angle and pitch, so that the from the main blades, to ,provideduplex blade line of junction 4 between the outer or tip blade units. 3thus formed, and the main blade I, is in true The outer blades are inthe form of extensions Y relationship t0 the bore 0f the Propeller, 01in 15 from the extremities of the -main blades, said other Words, thelines 4 formed by the intersecextensions being directed outwardly from,and tions of the outer blades 3 and the main blades forming angles withthe main blades, so as to l, are al1 OlSPOSed truly upon the periphery0f provide working surfaces beyond the radii of the en imaginaryCylinder having its aXiS COhCldent ggvlatter. with the axis of thepropeller and its shaft 5. V

The extensions thus formed, provide inclined The angle 0r Set 0f theOuter blades 3 in relasmaller or tip blades at the radial extremitiestion to the blades l, varies in accordance with of the main blades ofthe propeller, the extension the power used for propulsion. or width ofsaid tip blades from the main blades, The degree 0f extension 0f eachouter 0r tip g5 commencing at, and increasing from the outer blade 3,from a main blade l, 1S from nothing, 25 extremities of the leadingedges of the main starting at the outer extremity of the leading bladesaccording to the usual direction of rotaedge 6 of the latter, to adimension at the outer tion of the propeller, and increasing towards theextremity of the following edge 'I of the main following edges of themain blades, so that the blade l, approximating from one quarter to onegreatest extension or width of the tip blades, third of the width ofsaid main blade I, the 30 is at the following edges of the main blades,outer edge or extremity 8 of said outer or tip blade while the line ofjunction between each extension 3, being in the form of a shallow convexcurve I2. or tip blade and the main blade which carries it, 'Ihe surfacearea of each outer or tip blade 3, is disposed on the periphery of animaginary cylcan be equal to from one sixth to one eighth of inderhaving its axis coincident with the axis of the surface area of the mainblade I from which 35 the propeller and its shaft. the tip blade 3extends, said proportions being Other features are also comprised in theinhowever, merely approximate.

vention which will however, be more particularly 'I'he actual Width ordegree of extension of the described with the aid of the accompanyingouteror tip blades 3, the area of the latter, and

.40 drawing whereinz the angle at which said outer or tip blades 3 are40 Figure 1 is a rear elevation, set in relation to the main blades I,are each and Figure 2 a plan view, and all determined by the power used,the revolutions Figure 3 a side elevation of a propeller formedrequired, the work required to be done, and other according to theinvention, while conditions encountered in actual practice.

Figure 4 illustrates by means of a, diagram in- The surface 9 of eachouter or tip blade 3 45 corporating a series of sections, the formation'of `presented to the axis about which the propeller the outer blades,and rotates, is made hollow or concave through its Figures 5 and 6 are apart side elevation, and width or extension from the main blade I, thepart sectional view respectively, illustrating a degree of hollowness orconcavity increasing in a modification, and also the formation of theouter direction, from the least width or extension of 50 blades, bothviews being exaggerated to show the the blade 3 from the blade I, sothat the greatest Y hollowing of said blades. o degree of hollowness orconcavity of the blade 3 In carrying out the invention, the improved isat or close to the greatest Width or extension propeller or fan isformed to rotate through twoy of the latter from the blade I, (Figures4, 5, 6), distinct and separate zones, main blades I of the effect ofwhich is to allow Water to clear 65 itself without undue turbulence, andat the same time increase the thrust of the propeller.

In addition, for vessels used principally for towing and like purposes,each main blade l may be provided with two outer or tipi blades 3,(Figures 5 and. 6) each as before described, but set to opposite hands,so that increased efficiency of the propeller will alsoy be obtainedwhen same is reversed, as when a vessel is reducing way, or goingastern.

A second or additional outer or tip blade 3 may, or may not, have thesame set or angle in relation to the inner or main blade l, as the firstouter or tip blade.

Where two outer blades 3 are provided on main blade I, the space betweensaid outer blades 3,

can be left open, or be partly or completely filledV in, also the mainblades l will be adequately strengthened at the boss 2.

What I do claim and desire to obtain by Letters Patent of the UnitedStates of America iszl. A screw propeller comprising main bladesextending radially from the propeller boss, andY outer blades extendingfrom the main blades to provide duplex blade units, the main and outerblades forming a plurality of working surfaces, the outer blades beingin the form of extensions from the extremities of the main blades, saidextensions being directed outwardly from and forming angles with themain blades so as toprovide working surfaces from the radii of thelatter, the extension commencing at the outer extremity of the leadingedge of the main blade to the axis about which the propeller rotates,said faces being made hollow through their width or lextensionfrom themain blades the degree of concavity of the outer blades, increasing in adirection from Athe least width or extension of the outer blades, sothat the greatest degree of concavity, is at or close to the greatestwidth of the outer blades.

4. A screw propeller, as in claim 1, wherein two outer blades areprovided on each main blade, said outer blades being set to oppositehands.

5. A screw propeller as in claim l, wherein the line of junction betweeneach outer blade, and the main blade on which it is formed, is disposedupon the periphery of an imaginary cylinder having its axis coincidentwith the axis of the propeller and its shaft.

6. A screw propeller as in claim l wherein the outer edges of the outerblades are in the form of shallow convex curves.

GEORGE HARNETT lVICLEOD.

